Linear and rotational inductive position sensor

ABSTRACT

An apparatus for providing a signal related to a position of a part comprises an exciter coil, and a receiver coil disposed proximate to the exciter coil. The exciter coil generates magnetic flux when the exciter coil is energized by a source of electrical energy, such as an alternating current source. The receiver coil generates a receiver signal when the exciter coil is energized, due to an inductive coupling between the receiver coil and the exciter coil. The receiver coil has a plurality of sections, the inductive coupling tending to induce opposed voltages in at least two of the sections. Embodiments of the present invention include linear sensors, rotational sensors, and novel configurations for improved ratiometric sensing.

REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.11/474,685, filed Jun. 26, 2008, which claims priority to U.S.Provisional Application U.S. Ser. No. 60/694,384, filed Jun. 27, 2005,the entire content of each of which are incorporated herein byreference.

FIELD OF THE INVENTION

The invention relates to inductive position sensors, in particular tolinear sensors, and also to rotational position sensors

BACKGROUND OF THE INVENTION

Inductive rotational sensors are described in our co-pending patentapplication Ser. Nos. 11/399,150, 11/102,046, and 11/400,154, thecontents of all of which are incorporated herein by reference.

However, rotational sensors inherently restrict the distance of travelthat can be measured in certain applications, for example, electronicthrottle controls for automobiles. The use of linear sensors, or sensorssensitive to motion including a linear component, may provide moresensitive measurements over a longer travel range.

Signals from the receiver coils of inductive sensors are prone tovariation due to noise and manufacturing variations, for examplevariations in part separations. Improved sensors giving positionalsignals corrected for such common mode factors would be of greatcommercial interest, particularly for electronic throttle controlapplications, amongst many other possible applications.

SUMMARY OF THE INVENTION

An apparatus for providing a signal related to a position of a movablepart (movable referring to linear motion, rotation, or any combinationof motion types) comprises an exciter coil, and a receiver coil disposedproximate to the exciter coil. The exciter coil generates magnetic fluxwhen the exciter coil is energized by a source of electrical energy,such as an alternating current source. The receiver coil generates areceiver signal when the exciter coil is energized, due to an inductivecoupling between the receiver coil and the exciter coil. The receivercoil has a plurality of sections, the inductive coupling tending toinduce opposed voltages in at least two of the sections. A coil assemblyincludes the exciter coil, one or more receiver coils, and an optionalreference coil. The coil assembly may be formed on a substrate, forexample as metal tracks on a printed circuit board which can also beused to support an electronic circuit for signal processing.

The inductive coupling is modified by movement of the part so that thereceiver signal is related to the position of the part. For example, acoupler element may be mechanically coupled to the part, so that thecoupler element modifies the inductive coupling between the exciter coiland the receiver coil as it moves, so that the receiver signal isrelated to the coupler position and hence the part position. The couplerelement may comprise a metal plate, generally U-shaped metal structure,or other structure that modifies the inductive coupling.

In some embodiments of the present invention, the receiver coil isgenerally elongated, having a first end and a second end, a firstsection of the receiver coil having a major area proximate to first end,and a second section of the receiver coil having a major area closer tothe second end than the first section. The first section and the secondsection being having opposite winding directions, the inductive couplingbetween the exciter coil and the section inducing a first voltage, theinductive coupling between the exciter coil and the second sectioninducing a second voltage, the first and second signals being ofopposite phase, the receiver signal being a combination including thefirst voltage and the second voltage.

The exciter coil may have a generally elongated perimeter, such as asubstantially rectangular perimeter, and is generally planar for alinear sensor. The receiver coil(s) may lie in a plane parallel to thatof the exciter coil, and may be substantially coplanar with the excitercoil, or with an offset such as the width of a supporting printedcircuit board or other substrate. The exciter coil may have a generallycylindrical geometry for novel rotational sensors described herein.

In some examples of the present invention, the receiver coil includes atleast two sections. The sections may be triangular, diamond shaped, orother shape according to the nature of the position-sensitive signalrequired. Movement of the coupler element changes the relative degree ofinductive coupling between the exciter coil and the two or moresections. A linear position sensor provides a signal related to theposition of a part along a linear path. A rotational sensor may beconfigured so that the coil assembly (exciter, receiver, and optionalreference coils) are disposed on a generally cylindrical surface, andthe apparatus may be a rotational sensor for a shaft extending throughthe generally cylindrical surface. A reference signal, which can be usedfor correcting the receiver signals for common mode factors, may beobtained from a separate reference coil. In other examples, a pluralityof receiver coils are used, and the reference signal is obtained from acombination of signals obtained from the reference coils.

A reference coil may be configured to provide a signal substantiallyindependent of the position of the part when the exciter coil isenergized, and used in ratiometric signal processing (such as an analogdivision) to correct the position-dependent signals for common modefactors. The reference signal may also be used to estimate the gap oroffset between the coil assembly and a coupler element, for example todetermine a number of turns made. A reference coil, if used, may have afirst section located inside the exciter coil, and a one or more othersections located outside the exciter coil.

An electronic circuit may be provided operable to generate a positionalsignal that has a substantially linear relationship with the position tobe measured, either as a voltage versus linear position, voltage versusangular position, position along a curved path, or other position thatis a combination of linear motion and rotation. The part position may bea position of a pedal, movement of the pedal being mechanically coupledto the position of the coupler element, for example for electronicthrottle applications. The apparatus may comprise an electronic circuitoperable to providing a speed control to an engine.

Hence, an apparatus according to an embodiment of the present inventionfor determining a part position of a part, comprises: an exciter coil,the exciter coil generating magnetic flux when the exciter coil isenergized by a source of electrical energy; a plurality of receivercoils disposed proximate to the exciter coil, the receiver coilsgenerating a plurality of receiver signals when the exciter coil isenergized due to an inductive coupling between the receiver coils andthe exciter coil; a moveable coupler element having a positioncorrelated with the part position, the coupler element modifying theinductive coupling between the exciter coil and the receiver coils sothat each receiver signal is correlated with the part position; and anelectronic circuit providing a ratiometric signal derived from at leastone of the receiver signals and the reference signal. The electroniccircuit may generate the reference signal using at least two of thereceiver coils, so that the reference signal is substantiallyindependent of the coupler element position. Alternatively, a separatereference coil may be used.

The reference signal, however obtained, may be used to compensate forvariations in the receiver signal that is not correlated with thecoupler position, such as noise, supply voltage variations, andmanufacturing variations. The reference signal may be obtained usingnon-phase-sensitive rectification of at least two receiver signals, orfrom a separate reference coil.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C show a linear inductive sensor in plan view andcross-section, respectively;

FIGS. 2A-2B show a linear inductive sensor in which a distance modulatorhas an outside section;

FIGS. 3A-3B show two configurations of a coil that may be used for alinear modulator;

FIG. 4 shows a tilt compensating linear modulator;

FIG. 5 illustrates how electronic circuitry can be contained within theoutside section of a distance modulator;

FIG. 6 shows a distance modulator having a greater number of turns inthe outside section;

FIG. 7 shows a linear sensor in which the distance modulator has twosections outside the exciter coil;

FIGS. 5A-5C show an alternative configuration for a linear sensor;

FIG. 9 shows a distance modulator having a ground connection in theoutside section;

FIG. 10 shows the distance modulator having a ground connection in theinside section;

FIG. 11 shows a resonant circuit including the distance modulator;

FIG. 12 shows a transfer function of voltage output from the distancemodulator against gap;

FIGS. 13A-13B show transformation of a linear sensor configuration to acylindrical geometry for rotational sensor;

FIGS. 14A-14C illustrate transformations from linear to partialrotational configurations, and also for complete rotational sensors;

FIG. 15 shows a configuration for linear sensing over longer distances;

FIG. 16 shows an alternative configuration for linear sensing overlarger distances;

FIG. 17 shows signals from a 4-LM sensor coil configuration, the twosolid curves from two LMs, the two broken curves are the inversesignals;

FIGS. 18, 19A, and 19B illustrate further configurations for linearsensing over larger distances;

FIG. 20 illustrates non-phase sensitive rectification of LM signals togive a common mode signal;

FIGS. 21-23 illustrate further configurations for linear sensing, whichdo not need a separate DM coil;

FIG. 24 shows geometrical transformation to a cylindrical geometry, fora ratiometric rotational sensor without need for a separate DM coil;

FIGS. 25-26 illustrate application of cylindrical geometry rotationalsensors in ferromagnetic environments;

FIG. 27 illustrates a rotational sensor using a cylindrical geometrycoil assembly;

FIG. 28 illustrates attachment of a coupler to a rotating sleeve forrotational sensing with a cylindrical geometry; and

FIG. 29 illustrates a circuit for rectification to obtain a common modesignal.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to an inductive sensor for providing electricalsignals related to the position of a mechanical part, for example a partmoveable along a linear path. Embodiments of the invention include ahigh resolution linear sensor for use with an electronic throttlecontrol.

The part whose position is to be sensed, such as a pedal component, ismechanically coupled to a coupler element. The coupler element may be anelectrically conductive component, such as a metal plate, attached tothe part. For example, the coupler element may be a conductive plate, agenerally U-shaped conductor, a coil wound in a plane, or othercomponent capable of modifying the inductive coupling between coils. Thecoupler element may be an eddy plate that blocks the magnetic fluxcoupling between the exciter coil and the receiver coil(s), usually madeof a conducting material such as copper plate.

As the part moves, the coupler element moves with respect to at leasttwo coils. An exciter coil (which may also be called a transmitter coil)is connected to a sinusoidal alternating current source (excitationsource, such as a Colpitts oscillator) and generates magnetic flux.There is also a receiver coil, which in a linear sensor may be referredto as a linear modulator (LM). In a rotational sensor, the receiver coilmay be referred to as a rotational modulator (RM). The receiver coil mayalso be referred to as a sensor coil. In examples below, the term LM(linear modulator) is sometimes used for the receiver coils in arotation sensor, for example for coil assemblies having a generallycylindrical form.

The receiver coil is preferably formed in the same plane as the excitercoil. In response to the movement of the part to be sensed, the couplerelement is moved in a plane parallel to the two coils, and is closelyspaced with respect to the coils, so as to affects the degree ofinductive coupling between the exciter coil and the receiver coil, andthus the electrical current induced in the receiver coil by the AC fieldof the exciter coil.

In some embodiments of the invention, the receiver coil is wound as apair of coil sections connected in series. One coil section has a majorarea at one end of the coupling element motion and decreases in area toa minimum area at the other end of the coupler element motion. Thesecond coil section has a minimum area at the end of the motion at whichthe first coil section has a major area, and vice versa. The coilsections are wound so that the induced voltages in each section areopposed. For example, the sections of the receiver coil may be wound inopposed directions or handedness. A signal is generated from the seriescombination of the two receiver coil sections. When the coupler elementis positioned near one end of its travel, inductive coupling is greaterwith one section, and when the coupler element moves towards the otherend of its travel, inductive coupling to the first section diminisheswhile coupling to the second section increases. Thus, the receiversignal is correlated with the position of the coupler element. Usingphase sensitive rectification, a position signal may be obtained that issubstantially linear with position.

Any variation in the gap between the plane of the coupler element andthe plane on which the exciter and receiving coils are wound leads to avariation in the receiver signal. Other variations in receiver signalresult may be due to variations in the exciter supply voltage,temperature variations, extraneous electromagnetic signals (electricalnoise), and the like, generally termed common mode signals. A thirdsection, termed a distance modulator (DM), is formed on the device. Thiscoil may also be referred to as a reference coil. The distance modulatormay be a coil wound in such a way that its output signal issubstantially unaffected by the position of the coupler element, yet itsoutput signal will be affected by gap variation and the other commonmode signals.

The function of the distance modulator (DM) may also be provided by acombination of receiver coils, or sections of a receiver coil.

An electronic circuit can be used to obtain a position signal that isproportional to the part position. For example, using phase sensitiverectification of signals obtained from the receiver coil and thedistance modulator, followed by analog division, the common mode effectscan be eliminated. Alternatively, by subtracting the output of thedistance modulator coil from the output of the receiving coil, thereceiving coil signal is normalized by removing the common mode signals.

In one embodiment of the invention, the exciter coil and the receivingcoil are formed on a printed circuit board and the coupler element movesproximate to the circuit board. The distance modulator may be formed soas to tale advantage of the nature of the electromagnetic flux patterngenerated by the exciter coil. By forming the exciter coil so that theopposed sides of it extend along opposed longitudinal elements of thecircuit board, which is elongated in the direction of motion of thecoupler element, the fields which these coil sections generate willextend beyond the area of the exciter.

The distance modulator can be essentially formed as two (or more) serialsections, one disposed within the area defined by the exciter coil andat least one disposed externally of that area. This configuration allowslarger gain from the distance modulator coil, and accordingly a largerlength of linear travel of the coupler element. Since the flux densitythrough the inside region of the exciter coil will be greater than theflux density outside of that area, the section of the distance modulatorwhich extends outside of the bounds of the exciter coil may require alarger number of turns than the section within the exciter, to provideequal amplitudes from the two.

In an alternative embodiment of the invention the distance modulator hasthree sections, one inside section encompassed within the bounds of theexciter coil and two outside sections outside of the bounds of theexciter coil. This design tends to balance out the capacitive couplingbetween the exciter coil and the sections of the distance modulatorwhich are outside of the exciting coil.

An electronic circuit for providing a position signal from the variouscoil signals can be disposed on the circuit board within the bounds ofan outside section of the distance modulator coil, outside the confinesof the exciter coil.

Hence, an inductive linear position sensor for determining a partposition, the part having a coupler element attached thereto, comprises:an exciter coil; an alternating current excitation source for energizingthe exciter coil; a receiver coil configured so that the signal inducedin the receiver coil by the exciter coil field is a function of theposition of the coupler element; and (optionally) a distance modulatorcoil configured so that the signal is substantially independent of thecoupler element position but related to the gap between the couplerelement and the coil. The exciter coil(s), receiver coil(s), andoptional distance modulator coil(s) may collectively be referred to as acoil assembly, and may be formed on a printed circuit board.

An electronic circuit receives the various signals from the coilassembly and provides a position signal related to the coupler elementposition. The receiver coil may be formed within the limits of theexciting coil. The distance modulator may be formed partially within thelimits of the exciter coil and partially exterior of the limits of theexciter coil, and configured so that flux induced in the distancemodulator by the exciter coil is substantially independent of theposition of the coupler element, whereby the distance modulator outputmay be used to correct the receiver output to eliminate various commonmode signals and the effect of gap variation.

FIG. 1A shows a coil assembly according to an embodiment of the presentinvention, configured for linear inductive sensing. The coil assemblyincludes exciter coil 10, excitation source 12, a distance modulator (DMcoil) 14, a receiver coil, in this case a linear modulator (LM) coil 16,and coupler element 18. The exciter coil 10 is energized by theexcitation source and there is inductive coupling between the excitercoil and both the distance modulator 14 and linear modulator 16, whichinduces signals in both these coils. The signal from the distancemodulator is correlated with the gap between the DM and the couplerelement, and is substantially independent of the position of the couplerelement.

FIG. 1B shows the LM in isolation. The linear modulator includes twosections, which are indicated A and B in the figure, which areapproximate a pair of triangular windings having opposed windingdirections. The LM produces an output signal that is related to theposition of the coupler element. Hence, the voltages induced in eachsection tend to oppose, as in this case the LM is inside the excitercoil. The LM, or any receiver coil in any other example, is notnecessarily entirely inside the exciter, but can be approximately (orsubstantially) inside. As the coupler element moves from its indicatedposition at 18 to a position further to the left, the signal from the LMchanges as the contribution from the two sections A and B of the linearmodulator vary in proportion, due to different degrees of blocking ofthe inductive coupling by the coupler element.

The linear modulator has a differential structure, so called because inthe absence of the coupler element, the contributions from the twosubstantially triangular sections would tend to cancel out. Hence, theinductive coupling between the exciter coil and the linear modulatorvaries with the position of the coupler element 18. As the sections haveopposite winding directions, and both are within the exciter coil, thevoltages induced in each sections are opposed. This may be described byreferring to one section as forward and the other section as backward.One section (forward) tends to produce a signal in phase with theexciter, the other section (backward) produces a signal out of phase.Hence, phase sensitive rectification of the overall output signal of theLM allows the position of the coupler to be determined.

With the coupler element in the position shown, inductive couplingbetween the exciter coil and section A of the LM is blocked to a greaterdegree than the inductive coupling between the exciter coil and thesection B of the LM. As the coupler element moves to the left, therelative inductive coupling between the exciter coil and the twosections denoted A and B changes in proportion. If the coupler elementis in a left-most position while still remaining in the confines of theexciter coil, the inductive coupling with section B will be more greatlydininished. In the latter case, the output voltage from the LM will bedominated from the signal generated within section A.

The solid lines in these figures represent conductive elements, such aswires, ribbons, or other elongate electronic conductors. In preferredexamples, the lines represent tracks on a printed circuit board, whichmay be double-sided, multi-layered, or otherwise configured asappropriate to the application. The same circuit board may also supportan electronic circuit receiving signals from the coil, and possiblyincluding an oscillator for the excitation source. The crossing of twolines generally does not represent electrical interconnection. The coilsmay be formed on a substrate, such as a PCB, but in most examples thesubstrate is not shown.

FIG. 1C shows a section A-A′ of FIG. 1A in cross-section. This shows aprinted circuit board 19 supporting the exciter coil 10, DM 14, and LM16. The coupler element 18 is shown as being a substantially U-shaped incross-section, however other forms of coupler elements, such as a plate,may also be used. FIG. 1B illustrates the use of two exciter coils (10and 10′) and DM coils (14 and 14′); this increases also the reliabilityof the linear sensor by providing redundancy, but may not be requireddepending on the application. The two exciter coils are both labeled 10and are shown on opposed surfaces of the circuit board 19.

The coupler element may be formed from a folded copper plate, or mayalternatively comprise any electrically conducting material. TheU-shaped structure of the coupler element helps compensate for gapvariations, in particular tilt (as illustrated) so in this example thatthe distance modulator is a simple loop, and does not have adifferential structure. The coupler element compensates both gap andtilt in this configuration. The coil assembly is located at least inpart within the generally U-shaped coupler element.

FIG. 2A shows another coil configuration, which for example may be usedwith a coupler element that has a generally plate-shaped structure. Thecoil configuration comprises exciter coil 20, excitation source 22, DM24, and LM 26. The coupler element is shown at 28. In this example, theDM has an inside section substantially within the exciter coil, 24A, andan outside section 24B located outside of the exciter coil. The insidesection and outside section have forward and backward sections. In thiscontext, the terms forward and backward refer to the direction ofinduced voltage in each section due to inductive coupling with theexciter, and these are opposed as the flux direction outside the excitercoil is in the opposite direction from that inside the exciter coil. Themagnetic flux density from the exciter coil is typically stronger insidethe exciter coil, so that more turns may be required for the outsidesection of the DM.

The DM may not be sensitive enough to the gap distance, and one approachto this problem is to provide an unbalanced differential structure,which has a larger outside section than inside section, and/or moreturns in the outside section. However, other approaches may be used asdescribed later.

The signals from the inside section and outside section tend to cancelout, as part of a differential structure, and provide a signalcorrelated with the gap between the DM and exciter coil, in the axialdirection. However, the signal from the DM is generally substantiallyindependent of the position of the coupler element.

FIG. 2B shows the DM 24 alone, for clarity. The winding directions arethe same for the two sections of the differential structure, as the fluxdirection from the exciter coil is reversed going from inside theexciter coil to outside.

FIGS. 3A-3B show two possible LM coil configurations, the first coil 30having sections A and B, and the second coil 32 having sections labeledC and D. The series connection of the two coils will provide twice themagnitude of output voltage of a single coil, other factors beingidentical.

FIG. 4 shows a LM coil 34 formed as a series connection of the two coils30 and 32 illustrated in FIGS. 3A-3B. This configuration eliminates theeffects of tilt of the coupler element relative to the plane of the LM.Examples of the present invention may include such a tilt compensatingLM, particularly if the coupler element is substantially plate-like, nothaving a generally U-shaped configuration as shown in FIG. 1B. However,for illustrative simplicity, the simpler coil configuration, such asshown in FIG. 3 as coil 30, may be shown in various examples.

FIG. 5 shows exciter coil 50, excitation source 52, and DM 54, in a coilassembly similar to that shown in FIG. 2. The coupler element and LM arenot shown for clarity. This figure illustrates that electronic circuitrysuch as ASIC 56 can be located within the outside sections of the DMcoil 54. The electronic circuitry has little effect on magnetic flux,and hence on the inductive coupling between the exciter coil and the DM.

Electronic circuits used may be similar to those described in ourco-pending applications.

FIG. 6 shows a DM having more turns in the outside sections. The coilassembly comprises exciter coil 60, powered by excitation source 62, andDM 64. The coupler element and LM are not shown in this figure forclarity, but may be configured with respect to the exciter coil as shownabove in FIG. 2A. The DM 64 has a single turn in the inside section 64A,and three turns in the outside section 64B. The terms inside and outsiderefer to sections inside and outside respectively of the perimeter ofthe exciter coil 60.

The inside section has, for example, a forward direction and the outsidesection has a backward direction. The use of the terms forward andbackward simply indicates opposite senses of induced voltage within thesections.

FIG. 7 shows an exciter coil 70, excitation source 72, and DM coil 74.The DM configuration has an inside section (74A) and two outsidesections (74B and 74C), above and below the inside section, asillustrated. The DM has a differential structure, the outside sectionshaving, for example, a backwards section direction, and the insidesection having a forward section direction. Again, in this context, theterms forwards and backwards are used to indicate the relativedirections of induced voltages. The LM coil and coupler element are notshown for clarity.

If the DM has sections of one sense within the exciter coil, and one ormore sections outside the exciter coil that have an opposed sense, thecapacitive coupling with the exciter coil may be controlled. The DMdesign similar to that of FIG. 7 allows capacitive coupling effects tobe controlled, so that the capacitive coupling between the exciter coiland the DM is similar to that between the exciter coil and the LM. Moreparticularly, the capacitive coupling between the exciter coil and theforward/backwards sections of the DM cancel out. Referring again to FIG.6, capacitive coupling between the exciter coil and the inside andoutside sections of the DM may also be controlled, for example by thespacings between the turns of adjacent coil sections. This is discussedfurther in relation to FIG. 9.

FIG. 8A-8C shows another configuration comprising excitation coil 80,excitation source 82, DM 84 and LM 86. A possible position of thecoupler element is shown at 88, from where (as illustrated) it wouldmove left or right. This design has a smaller gain and also a restrictedrange of positional measurements compared to, for example, theconfiguration of FIG. 6. However, the DM can be completely confinedwithin the exciter coil.

FIG. 8B shows the DM 84 alone, for clarity. In this differentialstructure, there is an inside section defined by turns 84A, having awinding direction opposite to that of the outside section defined byturn 84B. In this example, both sections are inside the exciter coil,and so opposite turn directions are required for a differentialstructure.

FIG. 8C shows the LM 86 alone, for clarity. The LM has left and rightsections (the terms left and right are used for convenience with respectto this illustration). In other examples the LM may have otherstructures, such as an overall bow-tie shape, or other configurationswhere the inductive coupling between the sections is modified as thecoupler moves in such a manner as to allow the coupler position to bedetermined.

FIG. 9 shows a DM configuration with a ground connection to the outsidesection. The capacitive coupling is also affected by the location of theground connection to the DM. The figure shows excitation coil 90,excitation source 92, and DM 94. The LM 96 is shown dashed, for clarity.The DM has both an inside section (i.e. inside the excitation coil) andan outside section of opposed handedness (sense) outside the excitationcoil. In this case, the ground connection is made to the outsidesection. This tends to provide a higher impendence for capacitivecoupling induced currents, as currents generated proximate to theexciter coil have a longer length to go through before arriving at theground connection.

The inside section of the DM is a forward section, the outside sectionis backwards. The two sections of the LM are forwards and backwards, asshown upper left and lower right. In this example, to equalizecapacitive couplings with the DM and LM, the forward section turn of theDM is inside the backwards section turn of the LM.

The dashed oval shows a region where there is capacitive coupling of theexciter to the backward section of the LM (inside the exciter coil), andthe backward section of the DM (outside the exciter coil). In thisregion, the forward section of the DM is inside the LM, so capacitivecoupling is with the exciter is less important. Hence, the effects ofcapacitive coupling on the LM and DM can controlled, and may beequalized, so that capacitive coupling becomes another common mode typefactor, the effects of which on positional sensing can be largelyeliminated by ratiometric sensing.

FIG. 10 shows a configuration very similar to that of FIG. 9, but withthe ground connection made to the inside section. The figure showsexcitation coil 100, excitation source 102 and DM 104, the DM havinginside and outside sections of opposed senses, the ground connectionbeing made to the inside section. The LM is not shown, but may beconfigured similarly to FIG. 9, for example with section turn portion106 between the inside section of the DM and the exciter coil.

The configuration of FIG. 10 exhibits low impedance, compared to that ofFIG. 9, as the capacitive coupling induced currents has a shorterdistance to travel to ground.

For larger ranges of distance sensing, the relative size of the couplerelement compared with the area of the receiver coil tends to be small,for example, in comparison to rotational sensors where the couplerelement may typically be approximately half the size of the receivercoil (in this case, the rotational modulator). Due to the small size ofthe coupler element, the inductive coupling variation with the DM maynot be great enough for compensation of gap variations.

However, the gap sensitivity of the DM signal may be enhanced by forminga resonant circuit including the DM coil as an inductor. For example, acapacitor may be provided in series (or in parallel) to form theresonant circuit. Further, a resistor may be provided in series toadjust the quality factor (Q).

FIG. 11 shows a possible configuration, comprising exciter coil 110,excitation source 112, DM 114, resistor 116, and capacitors 118 and 119.The pair of capacitors provides a voltage divider for conditioning theinput to, for example, a ratiometric circuit. This circuit allows asmaller coupler element to be used.

Hence, an improved configuration for providing a common mode orreference signal reference coil comprises a reference coil generallyco-planar with the receiver coil, and at least one capacitor to form aresonant circuit, and optionally a resistor to modify the Q-factor ofthe resonant circuit.

FIG. 12 shows a representative curve 120 of induced voltage within theDM vs. gap. The inductance of the DM varies with the gap (physicalseparation) from the coupler element. In this example, the resonantfrequency is adjusted so that zero gap corresponds to a point just onthe downslope of this transfer function of voltage versus gap, i.e.slightly to the right of the resonant peak. This is the line labeled“zero gap”. The slope of the downslope may be varied by adjusting theresistor. Hence, the gap dependency of DM voltage output is enhanced bythe transfer function slope at the actual value of gap used (the pointlabeled “DM transfer function for gap”).

Examples described so far have generally been linear sensors; however,embodiments of the present invention also include partially orcompletely rotational position sensors.

FIG. 13A shows transformations of generally planar coil assemblies, forexample, that of FIG. 1A, to cylindrical forms. In this case, the planarform is shown as rectangle 130 and the cylindrical form would beprojected onto curved surface 132. The separation 134 may have minimaleffect.

The geometry of the linear sensor can be transformed to that of arotational sensor, which is tolerant gap variations due to the symmetryof gaps between the sensor windings (coil assembly) having a generallycylindrical form, and concentric coupler elements For example, see FIGS.27 and 28.

The sensor performs in a similar manner after such as geometricalchange. Preferably, the coupler has now two coupler elements (or eddyplates) displaced symmetrically as shown at 138 and 140. This type ofsensor can be used as a partial or complete rotational sensor, asdiscussed further below.

FIG. 13B shows associated transformations of a coupler element 134supported on object 136 to coupler element 138 having a generallycylindrical geometry.

FIGS. 14A-14C show transformations for rotational sensors, the rotationoccurring within the plane of the figures. For example, rectangle 142may correspond to the general shape of the coil assembly shown in FIG.1A, and this may be transformed into generally arc-shaped, but planarform 144. This type of transformation may be used to obtain a topologysuitable for a partial rotational sensor, i.e., a sensor sensitive tomovements that include both linear and rotational components.

FIGS. 14B and 14C show corresponding transformations to a topologysuitable for rotational sensors, including sensors for motion that iscompletely rotational with no linear component. For example, rectangle146 corresponds to the general shape of a coil assembly similar to thatof FIG. 1A, for example, transformed to circular shape 148. Similarly, arectangular coupler element 115 is transformed to one or more generallyarc shaped segments 152, supported by rotating object 154. In thisexample, rotation of object 154 is detected by the curved coil assembly148.

Linear sensors for longer linear movements can be obtained using alinear modulator coil (LMs) having more than two sections. The use oftwo LMs readily allows a continuous positional signal output to beobtained.

FIG. 15 shows a coil assembly including exciter coil 160, excitationsource 162, and LM including multiple sections 164, 166, 168 and 170. Inthis case, the adjacent sections have opposite handedness, for example,alternating anti-clockwise/clockwise sections. In this example, the LMmay be said to be a four-pole coil, having four poles or sections.

The coupler element may be a plate, or generally U-shaped structure, forexample, as shown in FIG. 1B. A possible coupler position is showndashed at 174. As illustrated, the coupler element moves in a generallyleft-to-right direction, modifying the inductive coupling between theexciter coil and the four sections.

FIG. 16 shows an alternative configuration having exciter coil 180,excitation source 182, and two four-pole LM coils, in whichcorresponding sections are overlapped by about half the area of eachsection. The second LM 184 is shown dashed to more clearly show itsposition relative to the first LM 182. The DM and coupler are not shown.

FIG. 17 shows four signals obtained from the two LMs of theconfiguration shown in FIG. 16, corresponding to signals and invertedsignals from each LM. Hence, a linear signal can be obtained by piecingtogether the indicated linear segments obtained from the normal andinverted signals, respectively. An electronic circuit for this type ofpiecing together of linear segments is further described in ourco-pending applications.

The curve LM#1 is obtained from the first LM, 182, and the curve LM#2 isobtained from second LM 184. LM#1′ and LM#2′ are the inverted versions.Each signal is periodic, with substantially linear sections shown asthicker sloping lines about a virtual ground (VG) level.

Inductive Sensors with DM Signal Provided by LM Coils

Using an electronic circuit, a distance signal can be generated from LMcoils, so that a separate DM coil is not necessary. The DM signal can beprovided by either one or more dedicated DM coils, or combination of LMcoils. In the latter case, the coil assembly may comprise an excitercoil and a number of coils of the same type, the signals from which canbe used to obtain both a DM signal and one or more LM signals. Aposition signal is generated by an electronic circuit, which is aratiometric signal obtained from the DM signal and a LM signal (whichmay be selected from a set of LM signals). The signal from each LMundergoes phase sensitive rectification to give a signal for linearposition determination, and a combination of non-phase-sensitiverectified signals are used to give a signal correlated with gap, but notwith coupler position.

FIG. 18 shows a coil assembly comprising exciter coil 190, withexcitation source 192, and a four-pole LM 194. The repeating structureof the LM means that a unique signal is only obtained over a limitedrange, indicated by the double arrow labeled “one modulus”.

With a given number of poles (sections), an LM can measure position overa certain distance, the modulus, outside of which the signal eitherbecomes nonlinear or repeats itself in the case of coupler elementtravel over additional sections. Measurement of an extended distance canbe measured by keeping track of the number of modulus distances traveledusing the repeating structure of the coil(s), or using other informationfrom which the number of modulus distances traveled can be determined.

FIG. 19A shows a configuration having four LMs, each LM being afour-pole coil. The four LMs are 194 (the same as shown in FIG. 18),196, 198, and 200. The exciter coil 190 is the same as in FIG. 18.

This combination of 4 LMs allows the common mode signal (gap or distancesignal) to be determined without the need for a specialized DM coil.

FIG. 19B shows another type of coil winding where return wires aretruncated at one side of the coil-assembly, to simplify connections.This approach to simplifying connections is known in the art. Thisconfiguration allows as many LM coils as needed for the different phasesof the signals for the signal processing. All the return wires of LMsare connected at the one end of coil set (at the left end).

FIGS. 18 and 19A show differential coils, from which signal picking, toobtain a linear positional response is simple, but there are many returnwires in the configuration of FIG. 19A, simplified in FIG. 19B. Analogratiometric signal processing may be used to obtain a positional signalcompensated for common mode factors.

The linear positional signal can be obtained from the signals providedby each LM. The gap signal, in other examples provided by a separate DMcoil, is in this case provided by non-phase-sensitive rectification oftwo or more individual LM coils signals, with subsequent combination ofthe rectified signals.

In this example, four LM coils such as shown in FIG. 18 are displaced a⅛ of the modulus distance relative to each other. Phase sensitiverectification is used to generate 4 signals from the LM coils, denotedLM1, LM2, LM3, and LM4. These four signals are used for findingposition. At the same time, the signal from each LM is rectified withoutphase sensitivity, as in RMS evaluation, denoted Vc1, Vc2, Vc3, and Vc4.The DM information is found from the combination of Vc1, Vc2, Vc3, andVc4 to correct for common mode factors such as gap or offset. TheDM-equivalent signal may also be referred to as a common mode signal orreference signal, and is the equivalent of the reference signaldescribed in our co-pending applications, and may similarly be used forratiometric sensing.

Hence the function of the DM coil is given by a combination of LM coils,which are also used for multi-modulus linear positioning. A separate“specialized” DM coil is not required. Instead, a circuit for non-phasesensitive rectification creates the common mode signal. Having obtainedthe common-mode signal, it can be used in ratiometric sensing.Consequently there is no physical DM coil, the coil body is simplified,and a true common mode signal is obtained which can be used forcommon-mode correction.

FIG. 20 is a graph showing phase-sensitive rectification of the LM1signal (line 210), which is substantially linear as a function ofcoupler position (the x-axis). The y axis is voltage, and VG is thevirtual ground The signals obtained by phase-insensitive rectificationof the LM1 and LM2 signals are shown as dashed lines 216 and 218.Combining (in this case adding) these signals gives a common mode signal214, which is substantially independent of coupler position. Division ofthe signal 210 by common mode signal 214 gives ratio-metric signal 212,which is the position signal provided by the sensor. The division may beeither analog or digital division, as described in our co-pendingapplications. The division operation is not necessarily an analogdivision, but may be performed in a digital manner via micro-computer.

Electronic circuits described in our co-pending applications may be usedin embodiments of the present invention, for example as adapted by theaddition of a non-phase-sensitive rectifier (and optionally a signalcombiner such as a voltage adder) to give the common mode signal, whichmay also be referred to as a reference signal, which is subsequentlyhandled like the reference signal described in our co-pendingapplications. For example, our co-pending U.S. provisional patentapplication, “Steering Angle Sensor” to the same inventor, filed Jun.26, 2006, is incorporated herein by reference. That application, inpart, describes a disk sensor with gap detecting to sense the multipleturns (beyond one modulus, where the modulus is the range over which aunique receiver coil signal can be obtained). Embodiments of the presentinvention include a cylindrical sensor with an offset detection to sensethe multiple turns (beyond one modulus), as described in relation toFIG. 27 below. The offset is substantially parallel to the central longaxis of the cylindrical form of the coil assembly, the axis of rotation.

FIG. 21 shows another configuration, including exciter coil 220,excitation source 222, first LM 224, second LM 226, third LM 228, andfourth LM 230. The figure shows the entire coil assembly at 232, withthe coupler element not shown. The figure also shows, for clarity, theLM coils individually, along with the handedness (forward of backward)of each section of the LMs. The first LM, 224, has two sections, and thesections of the other LMs are displaced relative to this. The other LMseach have three sections, but the first and last sections of each LM aretruncated at the ends of the coil assembly so as to be the same length,overall, as the first LM.

These LM windings provide a sinusoidal dependency of LM signal againstposition. For the compact use of inside area of the exciter coil, the LMcoil is modified as long as the balance of forward and backward windingarea is maintained. The balance means the ratio forward and backwardareas being such that the induced voltage of the coil is zero withoutthe coupler. The figure shows an example of 2 pole sensor windings forsinusoidal waves. The grounding scheme is modified in order to reducethe crossovers (the return wires of LM crossing the exciter) of LMreturn wires.

FIG. 22 shows a configuration similar to that of FIG. 21, the LMs havingsections of a slightly different shape. This includes exciter coil 240,excitation source 242, LM 244 (the upper diagram shows only the firstLM, the lower diagram shows all LMs), and other LMs 246, 248, and 250.This configuration gives of 2 pole LMs gives a triangular wavedependence of output voltage versus position.

FIG. 23 shows another configuration, similar to FIG. 21. The figureshows the entire coil configuration at 262, comprising exciter coil 250(with excitation source 252), LMs 254, 256, 258, and 260. In order togenerate a DM signal for the ratio-metric signal, all the LM signalsfrom (254, 256, 258, and 260) are rectified in phase insensitive mannerand combined to get the signal of 214 in FIG. 20. Any one of the signalof LMs can be rectified in phase sensitive manner to get the linearsignal as in 210 of FIG. 20.

Then the ratio (division 210 by 214) of the two signals can be obtainedas a sensor signal, which is free from any common mode signal, such asnoise, gap, offset (e.g. along an orthogonal direction to the gap), orEMI interference. This approach may be used for any example of DM-freeratio-metric sensing.

FIG. 24 shows a geometric transformation from a linear sensor to acylindrical geometry for a rotational sensor, Coil assembly 280 issimilar to that shown in FIG. 21 (coil assembly 232). If the substrateis flexible, for example a flexible polymer, the sensor may be formedinto cylindrical form 284. The electronic circuitry 282 may be the samein both cases. The coupler element is not shown, but may be a curvedplate rotating about central axis (X) either inside our outside the coilassembly. Two coupler elements may be used, as shown in FIG. 13B.

The configurations of FIGS. 21-24 can be used without a specialized DMcoil, as a common mode signal can be obtained by non-phase-sensitiverectification of the LM signals. The positional data is obtained usingphase sensitive rectification of the LM figures.

The cylindrical geometry of FIG. 24 is less sensitive to the effects offerromagnetic materials, either inside or outside the coil assembly.With this configuration of the sensing coils, the effects of surroundingor cores of ferromagnetic materials on the receiver coils can besignificantly reduced. If the DM coil and LM are the same geometricalshape, the coils respond in the same manner. Hence, by obtaining thereference signal from the LM coils, improved ratiometric sensing ispossible.

There may be edge-gap 286 between the two edges. If this gap can beeliminated effectively by, for example, an overlap, multi-turn sensorscan also be made.

FIG. 25 shows ferromagnetic material 286 outside the coil assembly 284.Cylindrical geometry coil assemblies, particularly without a specializedDM coil, work well in such situations.

FIG. 26 shows a ferromagnetic core 296 extending through the center of acoupler 294 comprising two coupler elements 290 and 292. However thenumber of couplers (in cylindrical transformation) might be arbitraryaccording to the number of the forward/backward winding pairs. Forexample, the sensor as in FIG. 21 that shows one pair offorward/backward winding pair, only one coupler is good, while in thecase of sensors as in FIG. 18 that shows two forward/backward windingpairs, two couplers are good, and so on.

This number of couplers of cylindrical transformation is quite differentfrom linear counter part, in which only one coupler can be used (ofcourse two couplers are used for two pairs of F/B windings). A coilassembly such as 284 (see FIG. 25) may be concentric with the coupler,and outside it. Again, cylindrical geometry coil assemblies,particularly without a specialized DM coil, work well in suchsituations.

FIG. 27 shows a partially exploded view of an assembly comprisingrotating shaft 310, with threaded outside surface 308. The sensor coilassembly 302, on a PCB, is supported on a threaded sleeve 300, theinside threaded surface of which engages with the threaded surface 308.The coupler 306 rotates with the shaft 310. An electronic circuit 304provides the positional signal. Sleeve 312 is used to attach the coupler306 to the rotating shaft 310. The offset between the coupler 306 andthe coil assembly changes as the shaft 310 rotates. The common modesignal can be used to measure the offset, and hence to determine thenumber of revolutions, with an LM being selected to provide a linearoutput against rotation angle. To determine the offset of the couplerwith respect to the sensor coil assembly PCB, the DM signal, or commonmode signal from the LM coils, can be detected, so that the angle beyondone modulus can be measured. The offset is generated by rotation of thethreaded sleeves, when the rotating shaft is turning. The DM signal willbe again ratio-metric over CR, and is at its maximum when the offset isminimum.

Hence, the offset of the coupler with respect to the sensor PCB varieswith rotation, and a reference signal can be determined (fromnon-phase-sensitive rectification of the receiver coils or using aspecialized reference coil, not shown here) so that the angle beyond onemodulus might be measured. The offset is generated by the rotation oftreaded surfaces, as the rotating shaft turns. The reference signal maybe ratiometric with respect to the exciter signal, and becomes a maximumwhen the offset is minimum.

FIG. 28 shows coupler 320 on the inside surface of a sleeve 324 havingan outside threaded surface, which rotates within the sensor coilassembly 322 formed on threaded sleeve (details not shown). Thisarrangement may be used in the configuration of FIG. 27.

FIG. 29 shows rectification of a signal for the gap or common modesignal. The circuit shows input of the exciter signal (CR) and thereceiver coil signal (RM, shown, or LM). The signals enter an analogmultiplier (344), and then is filtered and rectified. The output may beused as the common mode signal. Similar circuits may use signals fromtwo or more receiver coils.

Phase insensitive rectification can be applied to eliminate the diodedrop of common rectification. High frequency rectification can be donewith a Gilbert-cell and low frequency rectification may use the circuitof FIG. 29. The super-diodes can be used to rectify a slow movingsignal.

Patents, patent applications, or publications mentioned in thisspecification are incorporated herein by reference to the same extent asif each individual document was specifically and individually indicatedto be incorporated by reference. In particular, U.S. ProvisionalApplication U.S. Ser. No. 60/694,384, filed Jun. 27, 2005, isincorporated herein by reference. U.S. Provisional Application U.S. Ser.No. 60/618,448, filed Jun. 26, 2006 and U.S. patent application Ser.Nos. 11/399,150; 11/102,046; and 11/400,154, all to the same inventor,are incorporated herein by reference.

The invention is not restricted to the illustrative examples describedabove. Examples are not intended as limitations on the scope of theinvention. Methods, apparatus, compositions, and the like describedherein are exemplary and not intended as limitations on the scope of theinvention. Changes therein and other uses will occur to those skilled inthe art. The scope of the invention is defined by the scope of theclaims.

1. An apparatus for providing a signal related to a position of a part,the apparatus including: an exciter coil, the exciter coil generatingmagnetic flux when the exciter coil is energized by a source ofelectrical energy; a receiver coil, disposed proximate to the excitercoil, the receiver coil generating a receiver signal when the excitercoil is energized due to an inductive coupling between the receiver coiland the exciter coil, the receiver coil having a plurality of sections,the inductive coupling tending to induce opposed voltages in at leasttwo of the sections, the inductive coupling being modified by movementof the part so that the receiver signal is related to the position ofthe part.
 2. The apparatus of claim 1, further comprising a couplerelement mechanically coupled to the part, the coupler element modifyingthe inductive coupling between the exciter coil and the receiver coil sothat the receiver signal is related to the part position.
 3. Theapparatus of claim 1, wherein the coupler element comprises a metalplate.
 4. The apparatus of claim 3, wherein the coupler elementcomprises a generally U-shaped structure of an electrically conductingmaterial, a coil assembly including the exciter coil and receiver coilbeing at least in part being located within an interior portion of theU-shaped structure.
 5. The apparatus of claim 1, wherein the receivercoil is generally elongated, having a first end and a second end, afirst section of the receiver coil having a major area proximate tofirst end, a second section of the receiver coil having a major areacloser to the second end than the first section.
 6. The apparatus ofclaim 5, wherein the apparatus is a linear position sensor, theapparatus providing a signal related to the position of the part along alinear path, the receiver coil being generally elongated along thelinear path.
 7. The apparatus of claim 1, wherein the receiver coil hasa generally rectangular perimeter.
 8. The apparatus of claim 7, whereinthe receiver coil includes two generally triangular sections.
 9. Theapparatus of claim 1, wherein the apparatus is a rotational sensor, thereceiver coil and exciter coil being disposed on a generally cylindricalsubstrate.
 10. The apparatus of claim 9, further comprising a couplerelement moving along a generally circular path concentric to thegenerally cylindrical substrate.
 11. The apparatus of claim 9, theapparatus being a rotational sensor for a shaft extending through thegenerally cylindrical surface.
 12. The apparatus of claim 1, furthercomprising a reference coil, the reference coil providing a signalsubstantially independent of the position of the part when the excitercoil is energized. 13-27. (canceled)